Mirror device

ABSTRACT

A mirror device may include: a mirror including a base plate, a reflective film on a first surface of the base plate, and a plurality of first protrusions on a second surface of the base plate; a plurality of support parts for respectively supporting the plurality of the first protrusions, each support part having a groove formed therein for guiding the first protrusion; and a plurality of clamps for respectively pressing the plurality of the first protrusions against the respective grooves in the plurality of the support parts.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Japanese Patent ApplicationNo. 2011-032876 filed Feb. 18, 2011, and Japanese Patent Application No.2011-060899 filed Mar. 18, 2011.

BACKGROUND

1. Technical Field

This disclosure relates to a mirror device.

2. Related Art

In recent years, semiconductor production processes have become capableof producing semiconductor devices with increasingly fine feature sizes,as photolithography has been making rapid progress toward finerfabrication. In the next generation of semiconductor productionprocesses, microfabrication with feature sizes at 60 nm to 45 nm, andfurther, microfabrication with feature sizes of 32 nm or less will berequired. Accordingly, in order to meet the demand for microfabricationat 32 nm and beyond, for example, an exposure apparatus is expected tobe developed, in which a system for generating extreme ultraviolet (EUV)light at a wavelength of approximately 13 nm is combined with a reducedprojection reflective optical system.

Three kinds of systems for generating EUV light have been known ingeneral, which include an LPP (Laser Produced Plasma) type system inwhich plasma generated by irradiating a target material with a laserbeam is used, a DPP (Discharge Produced Plasma) type system in whichplasma generated by electric discharge is used, and an SR (SynchrotronRadiation) type system in which orbital radiation is used.

SUMMARY

A mirror device according to one aspect of this disclosure may include:a mirror including a base plate, a reflective film on a first surface ofthe base plate, and a plurality of first protrusions on a second surfaceof the base plate; a plurality of support parts for respectivelysupporting the plurality of the first protrusions, each support parthaving a groove for guiding the first protrusion; and a plurality ofclamps for respectively pressing the plurality of the first protrusionsagainst the respective grooves in the plurality of the support parts.

A mirror device according to another aspect of this disclosure mayinclude: a mirror including a base plate, a reflective film on a firstsurface of the base plate, and a plurality of base members on a secondsurface of the base plate, each of the base members having a grooveformed therein; a plurality of support parts for supporting theplurality of the base members respectively, each of the plurality ofbase parts including a protrusion to be guided along the groove formedin the base member; and a plurality of clamps for pushing the pluralityof the base members respectively against the plurality of theprotrusions.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, selected embodiments of this disclosure will be describedwith reference to the accompanying drawings.

FIG. 1 schematically illustrates the configuration of an exemplary LPPtype EUV light generation system.

FIG. 2 schematically illustrates the configuration of an EUV lightgeneration apparatus including mirror devices according to theembodiments of this disclosure.

FIG. 3A is a plan view illustrating an EUV collector mirror supported bymirror support mechanisms attached to a first support base plateaccording to a first embodiment; FIG. 3B is a sectional view, takenalong IIIB-IIIB plane, of the mirror support mechanisms shown in FIG.3A; and FIG. 3C is a side view of the mirror support mechanisms shown inFIG. 3A, viewed in the direction indicated with an arrow IIIC.

FIG. 4A is a side view illustrating a mirror support mechanism accordingto a second embodiment; and FIG. 4B is a sectional view, taken alongIVB-IVB plane, of the mirror support mechanism shown in FIG. 4A.

FIG. 5A is a side view illustrating a mirror support mechanism accordingto a third embodiment; and FIG. 5B is a sectional view, taken alongVB-VB plane, of the mirror support mechanism shown in FIG. 5A.

FIG. 6A is a side view illustrating a mirror support mechanism accordingto a fourth embodiment; and FIG. 6B is a sectional view, taken alongVIB-VIB plane, of the mirror support mechanism shown in FIG. 6A.

FIG. 7A is a side view illustrating a mirror support mechanism accordingto a fifth embodiment; and FIG. 7B is a sectional view, taken alongVIIB-VIIB plane, of the mirror support mechanism shown in FIG. 7A.

FIG. 8A is a side view illustrating a mirror support mechanism accordingto a sixth embodiment; and FIG. 8B is a sectional view, taken alongVIIIB-VIIIB plane, of the mirror support mechanism shown in FIG. 8A.

FIG. 9A is a side view illustrating a mirror support mechanism accordingto a seventh embodiment; and FIG. 9B is a sectional view, taken alongIXB-IXB plane, of the mirror support mechanism shown in FIG. 9A.

FIG. 10A is a side view illustrating a mirror support mechanismaccording to an eighth embodiment; FIG. 10B is a sectional view, takenalong XB-XB plane, of the mirror support mechanism shown in FIG. 10A;and FIG. 10C is a perspective view of a clamp according to the eighthembodiment.

FIG. 11A is a side view illustrating a mirror support mechanismaccording to a ninth embodiment; and FIG. 11B is a sectional view, takenalong XIB-XIB plane, of the mirror support mechanism shown in FIG. 11A.

FIG. 12A is a side view illustrating a mirror support mechanismaccording to a tenth embodiment; and FIG. 12B is a sectional view, takenalong XIIB-XIIB plane, of the mirror support mechanism shown in FIG.12A.

FIG. 13A is a side view illustrating a mirror support mechanismaccording to an eleventh embodiment; and FIG. 13B is a sectional view,taken along XIIIB-XIIIB plane, of the mirror support mechanism shown inFIG. 13A.

FIG. 14 is a side view illustrating a mirror support mechanism accordingto a twelfth embodiment.

FIG. 15 is a side view illustrating a mirror support mechanism accordingto a thirteenth embodiment.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, selected embodiments of this disclosure will be describedin detail with reference to the accompanying drawings. The embodimentsto be described below are merely illustrative in nature and do not limitthe scope of this disclosure. Further, the configuration and operationdescribed in each embodiment are not all essential in implementing thisdisclosure. Note that like elements are referenced by like referencenumerals or symbols and duplicate descriptions thereof will be omittedherein. The embodiments of this disclosure will be illustrated followingthe table of contents below.

1. Summary 2. Overview of EUV Light Generation System

2. 1 Configuration

2. 2 Operation

3. Mirror Device Having Support Part and Clamp

3. 1 Configuration

3. 2 Operation

4. Embodiments of Mirror Support Mechanism

4. 1 First Embodiment

4. 2 Second Embodiment

4. 3 Third Embodiment

4. 4 Fourth Embodiment

4. 5 Fifth Embodiment

4. 6 Sixth Embodiment

4. 7 Seventh Embodiment

4. 8 Eighth Embodiment

4. 9 Ninth Embodiment

4. 10 Tenth Embodiment

4. 11 Eleventh Embodiment

4. 12 Twelfth Embodiment

4. 13 Thirteenth Embodiment

1. SUMMARY

In the embodiments of this disclosure, a protrusion or a groove may beformed in a surface opposite to a reflective surface of an EUV collectormirror. A groove or a protrusion may be so formed in a support part forsupporting the EUV collector mirror to correspond to the protrusion andthe groove of the EUV collector mirror, respectively. Such protrusionand groove are fitted to each other to position the EUV collector mirrorwith high reproducibility. Further, when the EUV collector mirrorundergoes thermal expansion, the protrusion may slide along the grooveto suppress unbalanced deformation in the EUV collector mirror.

2. OVERVIEW OF EUV LIGHT GENERATION SYSTEM 2. 1 Configuration

FIG. 1 schematically illustrates the configuration of an exemplary LPPtype EUV light generation apparatus 1. The EUV light generationapparatus 1 may be used with at least one laser apparatus 3. In thisdisclosure, a system including the EUV light generation apparatus 1 andthe laser apparatus 3 may be referred to as an EUV light generationsystem 11. As illustrated in FIG. 1 and described in detail below, theEUV light generation apparatus 1 may include a chamber 2 and a targetsupply unit (droplet generator 26, for example). The chamber 2 may beairtightly sealed. The target supply unit may be mounted to the chamber2 so as to penetrate a wall of the chamber 2, for example. A targetmaterial to be supplied by the target supply unit may include, but notlimited to, tin, terbium, gadolinium, lithium, xenon, or any combinationthereof.

The chamber 2 may have at least one through-hole formed in the wallthereof, and a pulsed laser beam 32 may travel through the through-hole.Alternatively, the chamber 2 may be provided with a window 21, throughwhich the pulsed laser beam 32 may travel into the chamber 2. An EUVcollector mirror 23 having a spheroidal reflective surface may bedisposed inside the chamber 2, for example. The EUV collector mirror 23may have a multi-layered reflective film formed on a surface thereof.The reflective film comprises a molybdenum layer and a silicon layerlaminated alternately, for example. The EUV collector mirror 23 may havefirst and second foci, and may preferably be disposed such that thefirst focus lies in a plasma generation region 25 and the second focuslies in an intermediate focus (IF) 292 defined by the specification ofan exposure apparatus. The EUV collector mirror 23 may have athrough-hole 24 formed at the center thereof, and a pulsed laser beam 33may travel through the through-hole 24.

Referring again to FIG. 1, the EUV light generation apparatus 1 may beconnected to an EUV light generation control unit 5. Further, the EUVlight generation apparatus 1 may include a target sensor 4. The targetsensor 4 may have an imaging function and may detect at least one of thepresence, trajectory, and position of a target.

Further, the EUV light generation apparatus 1 may include a connection29 for allowing the interior of the chamber 2 and the interior of theexposure apparatus 6 to be in communication with each other. A partition291 provided with an aperture may be disposed inside the connection 29.The partition 291 may be disposed such that the second focus of the EUVcollector mirror 23 lies in the aperture formed in the partition 291.

The EUV light generation apparatus 1 may further include a laser beamdirection control unit 34, a laser beam focusing mirror 22, and a targetcollection unit 28 for collecting targets 27. The laser beam directioncontrol unit 34 may include an optical element for defining thedirection into which the laser beam travels and an actuator foradjusting the position and the posture of the optical element.

2. 2 Operation

With reference to FIG. 1, a pulsed laser beam 31 outputted from thelaser apparatus 3 may pass through the laser beam direction control unit34, and as a pulsed laser beam 32, may travel through the window 21 andenter the chamber 2. The pulsed laser beam 32 may travel inside thechamber 2 along at least one beam path, be reflected by the laser beamfocusing mirror 22, and strike at least one target 27, as a pulsed laserbeam 33.

The droplet generator 26 may output the targets 27 toward the plasmageneration region 25 inside the chamber 2. The target 27 may beirradiated with at least one pulse included in the pulsed laser beam 33.The target 27, which has been irradiated with the pulsed laser beam 33,may be turned into plasma, and rays of light including EUV light 252 maybe emitted from the plasma. The EUV light 252 may be reflectedselectively by the EUV collector mirror 23. The EUV light 252 reflectedby the EUV collector mirror 23 may travel through the intermediate focus292 and be outputted to the exposure apparatus 6. The target 27 may beirradiated with multiple pulses included in the pulsed laser beam 33.

The EUV light generation control unit 5 may control the EUV lightgeneration system 11. The EUV light generation control unit 5 mayprocess image data of the droplet 27 captured by the target sensor 4.Further, the EUV light generation control unit 5 may control at leastone of the timing at which the target 27 is outputted and the directioninto which the target 27 is outputted, for example. Furthermore, the EUVlight generation control unit 5 may control at least one of the timingat which the laser apparatus 3 oscillates, the direction in which thepulsed laser beam 31 travels, and the position at which the pulsed laserbeam 33 is focused, for example. The various controls mentioned aboveare merely examples, and other controls may be added as necessary.

3. MIRROR DEVICE HAVING SUPPORT PART AND CLAMP 3. 1 Configuration

FIG. 2 schematically illustrates the configuration of an EUV lightgeneration apparatus to which mirror devices according to theembodiments of this disclosure are applied. In the EUV light generationapparatus, the EUV collector mirror 23 may be supported by a mirrorsupport mechanism 7 inside the chamber 2. The mirror support mechanism 7may be supported by a first support base plate 81 inside the chamber 2.The first support base plate 81 may have a through-hole 84 formedtherein.

Inside the chamber 2, mirrors 22 a and 22 b, which collectivelyconstitute the laser beam focusing optical system 22, may be supportedby mirror holders 82 a and 82 b, respectively. The mirror holders 82 aand 82 b may both be attached to a second support base plate 83. Thesecond support base plate 83 may be supported by the first support baseplate 81 inside the chamber 2.

3. 2 Operation

The pulsed laser beam outputted from the laser apparatus 3 may bereflected by high-reflection mirrors 34 a and 34 b, which constitute thelaser beam direction control unit, and be directed so as to be incidenton the window 21 of the chamber 2. The pulsed laser beam transmittedthrough the window 21 may enter the chamber 2, be reflected by themirrors 22 a and 22 b, and be focused in the plasma generation region25.

The EUV collector mirror 23 may be heated by radiation heat from theplasma, or by laser beams scattered as the pulsed laser beam isscattered by the target material, to thereby undergo thermal expansion.However, according to the mirror support mechanism of the embodiments ofthis disclosure, the EUV collector mirror 23 may be positioned with highreproducibility, and thermal deformation in the EUV collector mirror 23may be suppressed.

4. EMBODIMENTS OF MIRROR SUPPORT MECHANISM 4. 1 First Embodiment

FIG. 3A is a plan view illustrating an EUV collector mirror supported bymirror support mechanisms attached to a first support base plateaccording to a first embodiment. FIG. 3B is a sectional view, takenalong IIIB-IIIB plane, of the mirror support mechanisms shown in FIG.3A. FIG. 3C is a side view of the mirror support mechanisms shown inFIG. 3A, viewed in the direction indicated with an arrow IIIC. Asillustrated in FIGS. 3A through 3C, three mirror support mechanisms 7,for example, attached to the first support base plate 81 may support theEUV collector mirror 23. The three mirror support mechanisms 7 may, forexample, be disposed along the periphery of the EUV collector mirror 23so as to be substantially equally spaced from one another in thecircumferential direction. Each mirror support mechanism 7 may include asupport part 70 and a clamp 74.

The support part 70 may comprises a support member 71 and a base member72 in which a groove is formed. The support member 71 may be positionedat a predetermined position in the first support base plate 81 and beattached therein. The base member 72 may be positioned at apredetermined position in the support member 71 and be attached therein.As illustrated in FIG. 3C, a V-shaped groove 721 may be formed, forexample in the base member 72 in a surface facing the EUV collectormirror 23. The three base members 72 may be arranged such that the threegrooves 721 formed in the three base members 72 extend radially based onthe rotational axis of the EUV collector mirror 23.

The EUV collector mirror 23 may include a mirror base 230 serving as abase member. A multi-layered film (multi-layered reflective film) 231may be formed on a surface of the mirror base 230. A plurality ofprotrusions 73 may be formed on the rear surface of the EUV collectormirror 23, that is, the side opposite to the surface where themulti-layered film 231 is formed. The number of the protrusions 73 maycorrespond to the number of the aforementioned grooves 721, and in thisembodiment, three protrusions 73 may be formed. As illustrated in FIG.3B, each protrusion 73 may be configured of a spherical body, part ofwhich is fitted into the mirror base 230, for example.

The clamp 74 may comprise an L-shaped member, for example. A first endof the clamp 74 may be attached to the support member 71 by a bolt 741.

A second end of the clamp 74 may be positioned so as to press theprotrusion 73 toward the groove 721 through a part of the mirror base230. With this, the mirror base 230 may be supported by the support part70. To be more specific, three holes 75 may be formed in the sidesurface of the mirror base 230, and the second ends of the three clamps74 may be inserted in the holes 75, respectively. A spherical recess 751may be formed in each hole 75 in a side surface toward the protrusion73. A ball 742, of which the diameter is smaller than the diameter ofthe recess 751, may be attached to the second end of the clamp 74. Theball 742 may be, when inserted in the recess 751, in point-contact withan inner surface of the recess 751 because the diameter of the ball 742is smaller than that of the recess 751.

With this, two points at which the protrusion 73 makes contact with theinner surface of the groove 721, the center of the spherical body of theprotrusion 73, and a point at which the ball 742 makes contact with theinner surface of the recess 751 are arranged on one hypothetical plane.The hypothetical plane perpendicularly extends from the first supportbase plate 81 toward the surface of the mirror base 230 through the twopoints at which the protrusion 73 makes contact with the inner surfaceof the groove 721, the center of the spherical body of the protrusion73, and the point at which the ball 742 makes contact with the innersurface of the recess 751 (see FIGS. 3B and 3C). Because of sucharrangement of the groove 721, the protrusion 73, and the ball 742, whenthe protrusion 73 having the spherical body slides along the groove 721,the clamp 74 bends. Even so, the ball 742 may hardly move within therecess 751, i.e., the point at which the ball 742 makes contact with therecess 751 may not move largely. As a result, the direction of the forcewith which the clamp 74 holds the mirror base 230 may be retainedsubstantially constant.

In the above configuration, the mirror base 230 is disposed so that thethree protrusions 73 engages respectively with the three grooves 721formed radially from the rotational axis (the center axis) of the EUVcollector mirror. Accordingly, the mirror base 230 can uniquely bepositioned. In general, when a disc-shaped body undergoes thermalexpansion, the deformation amount is larger in the radial direction.When the mirror base 230 is heated and undergoes thermal expansion, theprotrusions 73 may slide along the grooves 721 toward the periphery ofthe EUV collector mirror 23. In this way, the stress associated with thethermal expansion may be released in the direction toward the periphery.When the mirror base 230 is cooled and shrinks, the protrusions 73 mayslide along the grooves 721 toward the rotational axis of the EUVcollector mirror 23. As a result, even when the mirror base 230 expandsor shrinks, the spatial position of the rotational axis of the mirrorbase 230 may be prevented from being displaced.

As discussed above, even when the mirror base 230 expands or shrinks,the direction of the force with which the clamp 74 holds the mirror base230 may be retained substantially constant. Further, even when themirror base 230 expands or shrinks, the ball 742 may move along with therecess 751. Accordingly, even when the mirror base 230 expands orshrinks, the force added to the mirror base 230 may not fluctuatelargely, whereby the deformation in the mirror base 230 may besuppressed. The mirror base 230 may be easily removed by untighteningthe bolt 741 to remove the clamp 74.

4. 2 Second Embodiment

FIG. 4A is a side view illustrating a mirror support mechanism accordingto a second embodiment. FIG. 4B is a sectional view, taken along IVB-IVBplane, of the mirror support mechanism shown in FIG. 4A. FIGS. 4A and 4Billustrate only one mirror support mechanism 7A and only a part of themirror base 230. The general configuration of the mirror supportmechanism 7A and the mirror base 230 may be similar to that of themirror support mechanism 7 and the mirror base 230 according to thefirst embodiment.

The mirror support mechanism 7A according to the second embodiment maydiffer from the mirror support mechanism 7 in that a plunger 744, inplace of the ball 742, is formed at a mirror-side end of a clamp 74 a.The plunger 744 is a protrusion embedded with a spring. The plunger 744makes point-contact with the inner surface of the recess 751 to positionthe mirror-side end of the clamp 74 a with respect to the mirror base2301.

Further, the mirror support mechanism 7A may differ from the mirrorsupport mechanism 7 in that part of the clamp 74 a is configured of aleaf spring 743. At least part of the clamp 74 a extending in thedirection perpendicular to the first support base plate may be formed ofthe leaf spring 743. According to this configuration, the plunger 744may move easily in the direction toward the periphery of the mirror base230 as the leaf spring 743 bends. Accordingly, the plunger 744 mayeasily follow the expansion or shrinkage of the mirror base 230 causedby a change in temperature.

4. 3 Third Embodiment

FIG. 5A is a side view illustrating a mirror support mechanism accordingto a third embodiment. FIG. 5B is a sectional view, taken along VB-VBplane, of the mirror support mechanism shown in FIG. 5A. FIGS. 5A and 5Billustrate only one mirror support mechanism 7B and only a part of themirror base 230. The general configuration of the mirror supportmechanism 7B and the mirror base 230 may be similar to that of themirror support mechanism 7 and the mirror base 230 according to thefirst embodiment.

The mirror support mechanism 7B according to the third embodiment maydiffer from the mirror support mechanism 7A in the location of a leafspring 745 in a clamp 74 b. In the third embodiment, at least part ofthe clamp 74 b parallel to the first support base plate 81 may be formedof the leaf spring 745. According to this configuration, the plunger 744may move in the direction perpendicular to the first support base plate81 as the leaf spring 745 bends. Accordingly, the stress associated withthe expansion or shrinkage in the thickness direction of the mirror base230 may be released.

4. 4 Fourth Embodiment

FIG. 6A is a side view illustrating a mirror support mechanism accordingto a fourth embodiment. FIG. 6B is a sectional view, taken along VIB-VIBplane, of the mirror support mechanism shown in FIG. 6A. FIG. 6C is aPerspective view of a clamp according to the fourth embodiment. FIGS. 6Aand 6B illustrate only one mirror support mechanism 7C and only a partof the mirror base 230. The general configuration of the mirror supportmechanism 7C and the mirror base 230 may be similar to that of themirror support mechanism 7 and the mirror base 230 according to thefirst embodiment.

The mirror support mechanism 7C according to the fourth embodiment maydiffer from the mirror support mechanisms of the above embodiments inthe shape of a clamp 74 c. The end of the clamp 74 c, which is attachedto the base member 72, may bifurcate into two as shown in FIG. 6C. Theend of the clamp 74 c may be attached to an upper surface of the basemember 72 with bolts 741. In the above configuration, the center of thespherical body of the protrusion 73, the respective centers of the twobolts 741 attaching the clamp 74 c to the base member 72, and a point atwhich the plunger 744 makes contact with the mirror base 230 can bearranged in one hypothetical plane. The one hypothetical planeperpendicularly extends from the first support base plate 81 through thecenter of the protrusion 73, the respective centers of the two bolts741, and the point at which the plunger 744 makes contact with themirror base 230 (see FIGS. 6A and 6B). With this, the direction of theforce with which the clamp 74 c holds the mirror base 230 may beretained substantially constant.

4. 5 Fifth Embodiment

FIG. 7A is a side view illustrating a mirror support mechanism accordingto a fifth embodiment. FIG. 7B is a sectional view, taken alongVIIB-VIIB plane, of the mirror support mechanism shown in FIG. 7A. FIGS.7A and 7B illustrate only one mirror support mechanism 7C and only apart of the mirror base 230. The general configuration of the mirrorbase 230 may be similar to that of the mirror base 230 according to thefirst embodiment.

The mirror support mechanism 7D according to the fifth embodiment maydiffer from the mirror support mechanisms of the above embodiments inthe shape of a clamp 74 d. The end of the clamp 74 d, which is attachedto the base member 72, may bifurcate into two. The end of the clamp 74 dmay be positioned to a side surface of the base member 72 by pins 745.The clamp 74 d may be attached to another side surface of the basemember 72 by bolts 741. In the above configuration, the center of thespherical body of the protrusion 73, two points at which the clamp 74 dis positioned by the pins 745, and a point at which the plunger 744makes contact with the mirror base 230 can be arranged on onehypothetical plane. The one hypothetical plane perpendicularly extendsfrom the first support base plate 81 through the center of the sphericalbody of the protrusion 73, the two points at which the clamp 74 d ispositioned by the pins 745, and a point at which the plunger 744 makescontact with the mirror base 230. With this, the direction of the forcewith which the clamp 74 d holds the mirror base 230 may be retainedsubstantially constant.

4. 6 Sixth Embodiment

FIG. 8A is a side view illustrating a mirror support mechanism accordingto a sixth embodiment. FIG. 8B is a sectional view, taken alongVIIIB-VIIIB plane, of the mirror support mechanism shown in FIG. 8A.FIGS. 8A and 8B illustrate only one mirror support mechanism 7E and onlya part of the mirror base 230. The general configuration of the mirrorbase 230 may be similar to that of the mirror base 230 according to thefirst embodiment.

The mirror support mechanism 7E according to the sixth embodiment maydiffer from the mirror support mechanisms of the above embodiments inthe structure and the function of a clamp 74 e. The clamp 74 e accordingto the sixth embodiment may include a clamp body 746 having a inclinedsurface 748 formed at an end to be attached to the support part and apush-in part 747 (See FIG. 8B) having a inclined surface 749. The bolt741 may pass through a through-hole formed in the push-in part 747 and athrough-hole formed in the clamp body 746 and be screwed into thesupport member 71 so that the clamp body 746 and the push-in part 747are attached to the support part such that the inclined surfaces 748 and749 face each other. The through-hole in the clamp body 746 may beelongated in a direction perpendicular to the surface of the firstsupport base plate 81 as shown in FIG. 8B. Accordingly, the clamp body746 may be allowed to move in the direction perpendicular to the surfaceof the first support base plate 81.

In the above configuration, when the bolt 741 is screwed into thesupport member 71, the clamp body 746 is pushed toward the first supportbase plate 81 as the inclined surfaces 748 and 749 abut against eachother. With this, the direction of the force with which the plunger 744holds the mirror base 230 may be retained substantially constant whilethe retaining force is increased as well.

4. 7 Seventh Embodiment

FIG. 9A is a side view illustrating a mirror support mechanism accordingto a seventh embodiment. FIG. 9B is a sectional view, taken alongIXB-IXB plane, of the mirror support mechanism shown in FIG. 9A. FIGS.9A and 9B illustrate only one mirror support mechanism 7F and only apart of the mirror base 230.

The mirror support mechanism 7F according to the seventh embodiment maydiffer from the mirror support mechanisms of the above embodiments inthat the configuration of a protrusion 73 f differs from that of theprotrusion 73. The protrusion 73 f according to the seventh embodimentmay include seat 732 and a spherical body 733. The seat 732 may beattached to the rear surface of the mirror base 230. Part of thespherical body 733 may be fitted into the seat 732, and a hole 75 f maybe formed in the seat 732. In the seventh embodiment, the hole 75 f maynot need to be formed in the mirror base 230. One end of a clamp 74 fincluding the plunger 744 may be inserted into the hole 75 f, and thespherical body 733 may be pushed into the groove 721 by the plunger 744.The clamp 74 f may be configured similarly to the clamp 74 b shown inFIG. 5B. Since the spherical body 733 is configured separately from theseat 732, the spherical body 733 may be allowed to roll within thegroove 721. As a result, the friction force that the spherical body 733experiences with the groove 721 when the mirror base 230 expands orshrinks may be reduced.

4. 8 Eighth Embodiment

FIG. 10A is a side view illustrating a mirror support mechanismaccording to an eighth embodiment. FIG. 10B is a sectional view, takenalong XB-XB plane, of the mirror support mechanism shown in FIG. 10A.FIG. 10C is a perspective view of a clamp according to the eighthembodiment. FIGS. 10A and 10B illustrate only one mirror supportmechanism 7G and only a part of the mirror base 230. The generalconfiguration of the mirror base 230 may be similar to that of themirror base 230 according to the seventh embodiment.

The mirror support mechanism 7G according to the eighth embodiment maydiffer from the mirror support mechanisms of the above embodiments inthe shape of a clamp 74 g. In the eighth embodiment, both ends of theclamp 74 g may be attached to the upper surface of the base member 72 bybolts 741. Further, the middle portion of the clamp 74 g may be formedof a leaf spring 748. The middle portion of the clamp 74 g may beinserted into a slit 75 g of the seat 732, and the plunger 744 formed atthe middle portion of the clamp 74 g may be fitted into the recess 751formed in the slit 75 g. In the above configuration, the center of thespherical body 733 constituting the protrusion 73 g, the respectivecenters of points at which the clamp 74 g is attached to the base member72 with the two bolts 741, and a point at which the plunger 744 makescontact with the mirror base 230 can be arranged in one hypotheticalplane. The one hypothetical plane perpendicularly extends from the firstsupport base plate 81 through the center of the spherical body 733constituting the protrusion 73 g, the respective centers of points atwhich the clamp 74 g is attached to the base member 72 with the twobolts 741, and a point at which the plunger 744 makes contact with themirror base 230 (see FIGS. 10A and 10B). With this, the direction of theforce with which the clamp 74 g holds the mirror base 230 may beretained substantially constant.

4. 9 Ninth Embodiment

FIG. 11A is a side view illustrating a mirror support mechanismaccording to a ninth embodiment. FIG. 11B is a sectional view, takenalong XIB-XIB plane, of the mirror support mechanism shown in FIG. 11A.FIGS. 11A and 11B illustrate only one mirror support mechanism 7H andonly a part of the mirror base 230. The general configuration of themirror base 230 may be similar to that of the mirror base 230 accordingto the seventh embodiment.

The mirror support mechanism 7H according to the ninth embodiment maydiffer from the mirror support mechanisms of the above embodiments inthat a base member 72 h in which the groove 721 is formed is attached tothe rear surface of the mirror base 230 and a base member 76 h on whichthe protrusion 73 is formed is attached to the support member 71. Thegroove 721 may be formed in a surface of the base member 72 h to facethe support member 71. The protrusion 73 may be formed on a surface ofthe base member 76 h to face the mirror base 230.

The plunger 744 inside a hole 75 h formed in the base member 72 h maybias the base member 72 h such that the inner surface of the groove 721is pushed toward the center of the protrusion 73. A recess for theplunger 744 is not formed in the hole 75 h; thus, the plunger 744 mayslide against the inner surface of the hole 75 h.

In the above configuration, even when the mirror base 230 expands orshrinks due to a change in temperature, the base member 72 h may movealong the inner surface of the groove 721 with respect to the protrusion73. Further, even when the base member 72 h in which the hole 75 h isformed moves in accordance with the expansion or shrinkage of the mirrorbase 230, the plunger 744 may slide against the inner surface of thehole 75 h. Accordingly, even when the mirror base 230 expands orshrinks, the direction of the force with which the clamp 74 h holds themirror base 230 may be retained substantially constant. With this,unbalanced deformation in the mirror base 230 may be suppressed.

4. 10 Tenth Embodiment

FIG. 12A is a side view illustrating a mirror support mechanismaccording to a tenth embodiment. FIG. 12B is a sectional view, takenalong XIIB-XIIB plane, of the mirror support mechanism shown in FIG.12A. FIGS. 12A and 12B illustrate only one mirror support mechanism 7Iand only a part of the mirror base 230.

The mirror support mechanism 7I according to the tenth embodiment maydiffer from the mirror support mechanisms of the above embodiments inthat the mirror support mechanism 7I does not include a clamp butincludes a magnetic body, by which a protrusion 73 i and a base member72 i in which a groove is formed are attracted to each other. Forexample, the protrusion 73 i may be made of a ferromagnetic metalmaterial, such as iron, and the base member 72 i may be made of apermanent magnet such as a ferrite magnet or a neodymium magnet. Withthis, the ferromagnetic material and the magnet are attracted to eachother due to the magnetic force; thus, the protrusion 73 i may be pushedagainst the base member 72 i.

In the above configuration, even when the mirror base 230 expands orshrinks due to a change in temperature, the protrusion 73 i may slidealong the groove 721 while being pushed against the groove 721. Withthis, unbalanced deformation in the mirror base 230 may be suppressed.

4. 11 Eleventh Embodiment

FIG. 13A is a side view illustrating a mirror support mechanismaccording to an eleventh embodiment. FIG. 13B is a sectional view, takenalong XIIIB-XIIIB plane, of the mirror support mechanism shown in FIG.13A. FIGS. 13A and 13B illustrate only one mirror support mechanism 7Jand only a part of the mirror base 230. The general configuration of themirror support mechanism 7J and the mirror base 230 may be similar tothat of the mirror support mechanism 7I and the mirror base 230according to the tenth embodiment.

The mirror support mechanism 7J according to the eleventh embodiment maydiffer from the mirror support mechanisms of the first through ninthembodiments in that the mirror support mechanism 7J does not include aclamp but includes a magnetic body, by which a protrusion 73 j and abase member 72 j in which a groove is formed are attracted to eachother. For example, the base member 72 j may be made of a permanentmagnet such as a ferrite magnet or neodymium magnet and the protrusion73 j may be made of a ferromagnetic metal material, such as iron. Withthis, the ferromagnetic material and the magnet are attracted to eachother due to the magnetic force; thus, the base member 72 j may bepushed against the protrusion 73 j.

In the above configuration, even when the mirror base 230 expands orshrinks due to a change in temperature, the groove 721 may slide andmove with respect to the protrusion 73 j. With this, unbalanceddeformation in the mirror base 230 may be suppressed.

4. 12 Twelfth Embodiment

FIG. 14 is a side view illustrating a mirror support mechanism accordingto a twelfth embodiment. FIG. 14 illustrates only one mirror supportmechanism 7K and only a part of the mirror base 230. Further, FIG. 14illustrates only the support member 71, a base member 72 k, and theprotrusion 73 inside the mirror support mechanism 7K.

The mirror support mechanism 7K according to the twelfth embodiment maydiffer from the mirror support mechanisms of the above embodiments inthat the sectional shape of a groove 722 formed in the base member 72 kdoes not takes on a V-shape but the groove 722 has a flat bottom 723. Inthis way, the groove 722 may not need to be V-shaped as long as a groovehas a pair of inclined surfaces which converges toward the directioninto which the groove are pressurized by the protrusion 73.

4. 13 Thirteenth Embodiment

FIG. 15 is a side view illustrating a mirror support mechanism accordingto a thirteenth embodiment. FIG. 15 illustrates only one mirror supportmechanism 7L and only a part of the mirror base 230. Further, FIG. 15illustrates only the support member 71, the base member 72, and aprotrusion 731 inside the mirror support mechanism 7L.

The mirror support mechanism 7L according to the thirteenth embodimentmay differ from the mirror support mechanisms of the above embodimentsin that the protrusion 731 does not have a spherical body but takes on arod shape having a spherical portion at the tip thereof. Here, theprotrusion 731 does not need to be spherical in shape as long as theprotrusion 731 makes point-contact with the pair of inclined surfaces ofthe groove 721.

The above-described embodiments and the modifications thereof are merelyexamples for implementing this disclosure, and this disclosure is notlimited thereto. Making various modifications according to thespecifications or the like is within the scope of this disclosure, andit is apparent from the above description that other various embodimentsare possible within the scope of this disclosure. For example, themodifications illustrated for particular ones of the embodiments can beapplied to other embodiments as well (including the other embodimentsdescribed herein).

The terms used in this specification and the appended claims should beinterpreted as “non-limiting.” For example, the terms “include” and “beincluded” should be interpreted as “including the stated elements butnot being limited to the stated elements.” The term “have” should beinterpreted as “including the stated elements but not being limited tothe stated elements.” Further, the modifier “one (a/an)” should beinterpreted as “at least one” or “one or more.”

What is claimed is:
 1. A mirror device, comprising: a mirror including abase plate, a reflective film on a first surface of the base plate, anda plurality of first protrusions on a second surface of the base plate;a plurality of support parts for respectively supporting the pluralityof the first protrusions, each support part having a groove for guidingthe first protrusion; and a plurality of clamps for respectivelypressing the plurality of the first protrusions against the respectivegrooves in the plurality of the support parts.
 2. The mirror deviceaccording to claim 1, wherein the plurality of first protrusionscomprises three first protrusions, and the plurality of support partscomprises three support parts to support the three first protrusions,respectively.
 3. The mirror device according to claim 1, wherein themirror is substantially circular in shape, and the plurality of thegrooves are formed radially with respect to the rotational axis of themirror.
 4. The mirror device according to claim 1, wherein each of theplurality of the grooves is v-shaped, and each of the plurality of thefirst protrusions has a spherical portion that makes point-contact withthe pair of the inclined surfaces.
 5. The mirror device according toclaim 1, wherein each of the plurality of the first protrusionscomprises a spherical body, part of which is fitted in the secondsurface of the mirror.
 6. The mirror device according to claim 1,wherein each of the plurality of the grooves has a pair of taperedsurfaces, each of the plurality of the first protrusions comprises aspherical body, part of which is fitted in the second surface of themirror, each of the plurality of the clamps has a second protrusion forpushing a corresponding first protrusion against a corresponding groove,and a point at which force is applied to push the corresponding firstprotrusion by the second protrusion, two points at which the sphericalbody makes contact with the pair of tapered surfaces, and the center ofthe spherical body are arranged in one hypothetical plane.
 7. The mirrordevice according to claim 6, wherein the second surface of the mirror isopposite to the first surface, and a plurality of holes in which theplurality of the second protrusions are disposed respectively is formedin a third surface that intersects with the second surface of themirror.
 8. The mirror device according to claim 7, wherein a pluralityof recesses is formed in respective inner surfaces of the plurality ofholes for positioning the plurality of the second protrusionsrespectively, and a point at which the second protrusion makes contactwith the inner surface of the recess is the point at which force isapplied to push the corresponding first protrusion by the secondprotrusion, and arranged in the one hypothetical plane.
 9. A mirrordevice, comprising: a mirror including a base plate, a reflective filmon a first surface of the base plate, and a plurality of base members ona second surface of the base plate, each of the base members having agroove; a plurality of support parts for supporting the plurality of thebase members respectively, each of the plurality of support partsincluding a protrusion to be guided along the groove in the base member;and a plurality of clamps for pushing the plurality of the base membersrespectively against protrusions of the support parts.
 10. The mirrordevice according to claim 9, wherein the plurality of base memberscomprises three base members, and the plurality of support partscomprises three support parts to support the three first protrusions,respectively.
 11. The mirror device according to claim 9, wherein themirror is substantially circular in shape, and the plurality of thegrooves are formed radially with respect to the rotational axis of themirror.
 12. The mirror device according to claim 9, wherein each of theplurality of the grooves has a pair of inclined surfaces, and each ofthe plurality of the protrusions has a spherical portion that makespoint-contact with the pair of the inclined surfaces.
 13. The mirrordevice according to claim 9, wherein each of the plurality of theprotrusions has a spherical body, a part of which is fitted into thesupport part.